1. Field of the Invention
The present invention relates to wireless communications, and more specifically, a method and apparatus for transmitting and receiving data.
2. Related Art
3GPP (3rd Generation Partnership Project) TS (Technical Specification) Release 8-based LTE (long term evolution) is a key next-generation communication standard.
As set forth in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8),”, physical channels in LTE systems may be divided into downlink channels such as PDSCH (Physical Downlink Shared Channel) and PDCCH (Physical Downlink Control Channel) and uplink channels such as PUSCH (Physical Uplink Shared Channel) and PUCCH (Physical Uplink Control Channel).
PUCCH is an uplink control channel used for transmitting uplink control information including HARQ (hybrid automatic repeat request), ACK/NACK signals, CQI (Channel Quality Indicator), or SR (scheduling request).
Meanwhile, 3GPP LTE-A (advanced), an evolution version of 3GPP LTE, is being developed. 3GPP LTE-A systems adopt carrier aggregation and MIMO (multiple input multiple output) supportive of four or more antenna ports.
Carrier aggregation uses multiple component carriers. Each component carrier is defined with a center frequency and a bandwidth. One downlink component carrier or a pair of uplink component carrier and downlink component carrier corresponds to one cell. If a UE receives a service using a plurality of downlink CCs, the UE may be said to receive the service from a plurality of serving cells.
TDD (time division duplex) systems use the same frequency for downlink and uplink. Accordingly, an uplink sub-frame is associated with one or more downlink sub-frames. The term “association” means that transmission/reception in a downlink sub-frame are associated with transmission/reception in an uplink sub-frame. For example, when receiving transport blocks in a plurality of sub-frames, the UE transmits HARQs or ACKs/NACKs for the transport blocks in an uplink sub-frame associated with the plurality of downlink sub-frames.